Sciencemadness Discussion Board - How to increase the temperature of a slow burning fuel?

How to increase the temperature of a slow burning fuel?

AJKOER - 23-2-2015 at 11:05

I have a slow burning fuel and wish to increase the flame temperature.

One idea is to add, say, Aluminum powder or a Mg/Al alloy, but not sure of, say an alcohol fuel, could be hot enough to make use of the metal additive.

Other than that, no ideas.

I do not wish to add anything like KClO3 as it would likely increase combustion rate and perhaps introduce a potential explosion hazard.

Other suggestions please!

[Edited on 23-2-2015 by AJKOER]

aga - 23-2-2015 at 11:14

Heat it.

deltaH - 23-2-2015 at 11:17

nitrate your fuel? Partial nitration can improve combustion but not necessarily = explosive.

Even *just* mixing in some nitric acid might help, though without specifics it's very hard to answer this question.

[Edited on 23-2-2015 by deltaH]

AJKOER - 23-2-2015 at 11:21

Quote: Originally posted by aga

Heat it.

Actually, I was considering allowing a heat source (via, for example, thermal conduction) into the fuel mix.

deltaH - 23-2-2015 at 11:24

You can also use a heat exchange of the combustion products to preheat the feed air

AJKOER - 23-2-2015 at 11:26

Quote: Originally posted by deltaH

nitrate your fuel? Partial nitration can improve combustion but not necessarily = explosive.

Even *just* mixing in some nitric acid might help, though without specifics it's very hard to answer this question.

[Edited on 23-2-2015 by deltaH]

Delta, I also was thinking about KNO3, but would not the burn rate (a significant constraint, required to increase only very moderately) accordingly rapidly increase as well?

deltaH - 23-2-2015 at 11:36

Quote: Originally posted by AJKOER

Quote: Originally posted by deltaH

Delta, I also was thinking about KNO3, but would not the burn rate (a significant constraint, required to increase only very moderately) accordingly rapidly increase as well?

Well, ANY increase in temperature MUST cause an increase in rate... simple chemical kinetics. Under mass transfer limitation, there is also an increase, simply not as much.

A partial nitration is a great way to speed up temperature and rate of fuel burn, countless examples.

If you're going to do this on large scale, consider cheaper nitrates like calcium nitrate or sodium nitrate, although bulk fertiliser KNO3 isn't *that* expensive. Can also consider nitric acid itself.

***
Maybe not explained as well as I should, improving the OB of the fuel by introducing nitrate can help increase the temperature (just as burning with air enriched in O2 would), the increase in rate though can be kept from extreme by ensuring controlling the mass transfer, i.e. making it hard for air to get to the fuel. You can lookup the theory of "external mass transfer limitation", there's simple equations for that.

[Edited on 23-2-2015 by deltaH]

deltaH - 23-2-2015 at 11:54

For example, if it's a solid, then the pellet size of the fuel will affect the mass transfer rate and can help so that rates don't get too high (but they must nevertheless climb with an increase in temperature!).

Loptr - 23-2-2015 at 11:55

If this is a pyrotechnic question, you could add a higher temperature oxidizer, such as barium sulfate. I have also heard that adding silicon, boron, etc., will also increase the temperature.

I would guess it really depends on what you are trying to do.

[Edited on 23-2-2015 by Loptr]

deltaH - 23-2-2015 at 11:57

If it's a solid, you can also consider adding hexamine, it has a very high heat of combustion for a solid, also fuel tablets with the added trioxane.

[Edited on 23-2-2015 by deltaH]

Zombie - 23-2-2015 at 12:03

Wouldn't it help if we knew what the fuel was?

This seems rather vague.

Gasoline, wood, coal, ethanol, paper, dirt?

deltaH - 23-2-2015 at 12:04

Obviously it's soy beans

Bert - 23-2-2015 at 12:05

Thermodynamics...

Either add/retain more energy in the system (preheat reactants? Insulate reaction chamber?), react more of the materials chosen per unit of time- Or change the reactants to higher output materials.

If you have a particular case or application in mind, state it and we can make recommendations.

As question stands, not much more to be said.

AJKOER - 23-2-2015 at 14:23

As the opening thread suggests, by example, an alcohol (which could be converted into a gel like substance). The goal is an improved alcohol like lamp with a modest reduction in time to refill with higher temperature applications.

Factors include cost, but more so safety issues, including, for example, gas emmissions so no barium salts, or possible small amounts of ethyl nitrate/nitrite per the addition of HNO3, ...

Sorry for lack of details, but I did want to encourage conceptual thinking to suggest how to redesign, which I certainly obtained (thanks).

I could also just infuse the alcohol with N2O (as I have experimented with previously and reported on SM). The apparent modest benefit (at some cost) is achieved by the increase in oxygen content, but there is a small chance of an explosion with an electro-static discharge, so not totally satisfactory either (see this link to the Energetic Material section of SM: http://www.sciencemadness.org/talk/viewthread.php?tid=32334 ).

If anyone has further comments, please continue with the dialog.

[Edited on 23-2-2015 by AJKOER]

Sulaiman - 23-2-2015 at 15:15

a bit sideways but,
if you could partially combust/oxidise the fuel to produce carbon monoxide
then burn the CO with air you will get a much higher temperature,
unfortunately I've no idea how to efficiently and reliably partially combust the fuel to get CO

[Edited on 23-2-2015 by Sulaiman]

Zombie - 23-2-2015 at 16:05

What about simply pressurizing it w/ Nitros oxide, and adapting a burner assembly?

AJKOER - 23-2-2015 at 16:57

Quote: Originally posted by Zombie

What about simply pressurizing it w/ Nitros oxide, and adapting a burner assembly?

Per my source reference on N2O infused fuels (see link above), and a video I barely remember on a rocket launch using such a monofuel with ignition via a spark plug hooked up to a car battery, "adapting" a burner assembly encompasses electrical wiring as well.

Note, sometimes those amateur rockets using the N2O infused fuels just go boom! Having your burner assembly on rare occasions behaving similarly is a problem

.

[Edited on 24-2-2015 by AJKOER]

AJKOER - 23-2-2015 at 17:16

Quote: Originally posted by Sulaiman

a bit sideways but,
if you could partially combust/oxidise the fuel to produce carbon monoxide
then burn the CO with air you will get a much higher temperature,
unfortunately I've no idea how to efficiently and reliably partially combust the fuel to get CO

[Edited on 23-2-2015 by Sulaiman]

Actually, your idea is interesting as CO can be chemically created at a reasonable temperature also (see, for example, http://chem-guide.blogspot.com/2010/04/laboratory-preparatio... ).

However, still not that easily.

Probably, given toxicity issues with the CO, only could employ the Carbon monoxide burner in a fume hood in any event.

[Edited on 24-2-2015 by AJKOER]

Zombie - 23-2-2015 at 17:19

Somehow I missed that post.

AJKOER - 23-2-2015 at 17:57

Quote: Originally posted by Zombie

Somehow I missed that post.

Yes, one of my more energetic threads.

Sulaiman - 23-2-2015 at 19:00

Calcium carbide + water = acetylene
Hydrogen peroxide + catalyst = oxygen

when I was a teenager I used this for a hot flame
(carbide used to be widely available for portable and bicycle gas lamps)
using MnO2 as the catalyst.

I had a brilliant idea ...
put the calcium carbide in the H2O2 and maybe it would catalyse and make acetylene simultaneously .....
IT WORKED !
at first a yellow flame, then the flame got hotter and hotter,
and louder and louder,
and the pitch of the flame got higher and higher,
and smaller and smaller ..... BOOM

A GLASSWARE SHRAPNEL BOMB.
luckily I was young and immortal so no real harm done.

Anyway, if you're going the synthesis route
oxy-acetylene gives a really hot flame using low toxicity chemicals
I believe calcium carbide synthesis and storage is do-able,
and H2O2 is widely available.
OR
would just using oxygen gas with your fuel give enough increased temperature?

Zombie - 23-2-2015 at 19:12

There's a thought. What about Calcium Carbide, and water/alcohol?

I didn't look up the heat energy so please excuse my eagerness.

j_sum1 - 23-2-2015 at 19:26

My favourite way of producing oxygen is cobalt chloride catalyst in hypochlorite bleach. Works a charm. I have easier access to bleach than peroxide and so this is very accessible.
That's if acetylene - oxygen is a sensible way for you to go.

Bert - 23-2-2015 at 21:23

Quote:

Factors include cost, but more so safety issues, including, for example, gas emmissions so no barium salts, or possible small amounts of ethyl nitrate/nitrite per the addition of HNO3, ...

Do you intend for this to be useable by anyone?

If you're planning on turning loose a commercial product to the average consumer, CO or acetylene generators are asking for a problem. Potentially high explosive mixtures in a product intended to be set on fire indoors would be something else to avoid- Sure, they USUALLY deflagrate. Then some idiot drops one while burning and tries to stamp out the fire... Bad things happened to a few GI's using burning chunks of C4 for ration heating under those conditions.

Am I getting old? I'm so boring.

Could you define your goal more tightly. Say, how much water do you want to bring to a boil in what amount of time? Or what wattage equivalent electric element would you like to replace, and how long between re-fueling is acceptable?

AJKOER - 24-2-2015 at 05:34

I should refrain the general factors for consideration as relating to cost, safety and performance with constraints on fuel availability (like CaC2, for example, versus alcohol, hexamine, charcoal,..) and vessel size/burn duration requirements. Also, one may be able to adjust fuel and O2 levels for tailoring to specific tasks.

That being said, I can envision times where one would sacrifice cost versus performance, and for some of us, hopefully on rare occasions only, even safety concerns. So the factors possibly express more of an approximate relation (inverse) to each other than absolutes. Going commercial creates a whole new burden with respect to safety and legal liability issues, of course, but does provide the luxury of scale and possible expanded access to things like CaC2,..

For those with some experience on using outdoor fuel tablets, for example, their opinion on safety is welcomed as is those with experience on indoor use of canned heat products and possible toxicity issues.

We may also be able to agree on ruling out "using burning chunks of C4"

.

[Edited on 24-2-2015 by AJKOER]

deltaH - 24-2-2015 at 08:21

Quote: Originally posted by Bert

... Bad things happened to a few GI's using burning chunks of C4 for ration heating under those conditions.

That was tested on mythbusters and 'busted'.

AJKOER, okay, now I get the idea of what you're trying to do, wasn't sure if your fuel was liquid or solid.

For liquids, if it's a volatile alcohol, what you ideally need is another liquid fuel that has higher heat of combustion AND either (i) boils very close to the boiling point of your alcohol or whatever mix is there or (ii) forms an azeotrope with your alcohol. This is important or you mixture will burn off more of the volatile component at first and so change flame characteristics as it goes, which is bad for gel fuels that you're lighting as a 'batch' and burning for some time. This is not a problem for direct injection combustion where everything is volatilised anyhow.

I would simply blend with hydrocarbons, remember also that nitrogen in the fuel can create fuel NOx, so not appropriate for indoors. I'd stick to hydrocarbons and oxygenates to be safe.

As for azeotropes, a hydrocarbon and alcohol is more likely to result in an azeotrope than an ether and alcohol, for example, but an ether and alcohol where the boiling point of the ether used is close to the alcohol is also fine. Again, you would also need to cross reference with things that can be commercially bought cheaply of course, makes everything extra interesting

blogfast25 - 24-2-2015 at 08:31

Quote: Originally posted by deltaH

Quote: Originally posted by Bert

... Bad things happened to a few GI's using burning chunks of C4 for ration heating under those conditions.

That was tested on mythbusters and 'busted'.

They actually busted something that couldn't be busted with a piece of paper, a pencil and 5 minutes of time?

Bert - 24-2-2015 at 08:51

"Mythbusters" is entertainment, not statistically valid research. To me, they are mostly annoying- Please just give their production budget to some actual engineers, you could then have useful research.

I have watched them massively fail to get the point, "prove" the false and "bust" the true off of a far too limited number of trials, often conducted within insanely wrong, ignorant parameters... Hopeless.

blogfast25 - 24-2-2015 at 08:59

Quote: Originally posted by Bert

"Mythbusters" is entertainment, not statistically valid research. To me, they are mostly annoying- Please just give their production budget to some actual engineers, you could then have useful research.

I have watched them massively fail to get the point, "prove" the false and "bust" the true off of a far too limited number of trials, often conducted within insanely wrong, ignorant parameters... Hopeless.

Can't disagree with a syllable there. Rather comically the Pretzeldent felt he had to endorse MB. MB thought that was kewl. Very kewl for their bottom line, that is.

deltaH - 24-2-2015 at 09:20

Bert, are there any documented cases of bad things happening to GI's you can point to concerning this myth?

[Edited on 24-2-2015 by deltaH]

Fulmen - 24-2-2015 at 09:39

I agree, although they usually do good (and fun) experiments they sometimes lack a couple of engineers. Their biggest problem is that the show can't deal with the statistically improbable, even though I expect they do a lot more work than what is shown. Results in the improbable range are also not viewer friendly, they want a definitive answer. I wish they could be a little more selective in their choice of myths sometimes, but it's still more fun than most other shows out there.

blogfast25 - 24-2-2015 at 10:02

Quote: Originally posted by Fulmen

[...] but it's still more fun than most other shows out there.

Disagree. Watching paint dry is more interesting in most cases. Not to mention that annoying self-congratulatory tone, 'aren't we cool?' (A. NO!) and infantile presentation. It's a money spinner and that's its only purpose.

Some claim it's 'educational'? How? By proving you can't catapult illegal aliens across the border? That cars can't be made to fly by strapping fire crackers to them?

[Edited on 24-2-2015 by blogfast25]

Zombie - 24-2-2015 at 11:06

I would pay to see either one of those attempted!

Endo - 24-2-2015 at 13:49

You could look at some of the gelling agents used in Napalm. I believe that some of these could be used to give a hotter burning flame, probably at the cost of adding some smell... Aluminum salts of Napthalene come to mind.

jock88 - 24-2-2015 at 15:07

I believe placing stuff like carbon black can increase burning rate due to its ability to absorb radiation as the fuel burns and thereby increases the temperature of the burning front.

blogfast25 - 25-2-2015 at 11:27

Quote: Originally posted by jock88

I believe placing stuff like carbon black can increase burning rate due to its ability to absorb radiation as the fuel burns and thereby increases the temperature of the burning front.

I don't think you've thought this through very well. Adding carbon means adding fuel. And carbon burns very hot (compare charcoal fired furnaces to gas fired ones, for instance).

But it's ability to 'absorb radiation' has nothing to do with anything. It has to return that radiation otherwise it would heat to beyond the temperature of the fire, at which point the Second Law dictates it must start losing heat to that environment again.

Carbon adds kJ of combustion Enthalpy to the burning object but nothing more.

[Edited on 25-2-2015 by blogfast25]

AJKOER - 25-2-2015 at 11:39

Thanks for all of the suggestions.

I also have an idea of dissolving sulfur in Toluene (highly flammable, see comments by Woelen on a safe procedure to dissolve the sulfur at http://www.chemicalforums.com/index.php?topic=5831.0 ). I am thinking of employing the mix in a burner in small amounts with an added air stream.

An issue appears that I have not as of yet secured a convenient and reasonably priced supply of Toluene.

Interesting also, there is a comment on the internet of using Toluene as an octane booster.

Molecular Manipulations - 25-2-2015 at 12:01

Quote: Originally posted by AJKOER

Going commercial creates a whole new burden with respect to safety and legal liability issues, of course, but does provide the luxury of scale and possible expanded access to things like CaC2,..

What are you going to do with this? Are you trying to make a commercial product? If so, I don't think people are going to want sulfur dioxide to be a combustion product. Also, what advantage does sulfur dissolved in toluene have over pure toluene?

AJKOER - 25-2-2015 at 14:21

Quote: Originally posted by Molecular Manipulations

Quote: Originally posted by AJKOER

Going commercial creates a whole new burden with respect to safety and legal liability issues, of course, but does provide the luxury of scale and possible expanded access to things like CaC2,..

No, this is just an experiment (that I am not likely to forget) and certainly not intended to be a commercial product.

Reducing the sulfur content of a fuel will reduce its heat content (see, for example, http://www.eia.gov/todayinenergy/detail.cfm?id=20092 ) and increasing the opposite effect.

[Edited on 26-2-2015 by AJKOER]